Electron discharge device



Sept. 15, 1936. K, sTElMEL 2,054,452

" ELECTRON DISCHARGE DEVICE 7 Filed June 29, 1934 2 Sheets-Sheet 1 INVENTOR KARL STEI M EL ATTO RN EY Sept. 15, 1936. K. STEIMEL ELECTRON DISCHARGE DEVICE Filed June 29, 1934 2 Sheets-Sheet 2 llll ll- INVENTOR v KARL STEIMEL A TTORNEY i i Patented Sept. 15 1936 UNITED STTES FATE OFFICE ELECTRON DISCHARGE DEVICE Germany Application June 29, 1934, Serial No. 732,991 In Germany July 5, 1933 7 Claims.

My invention relates to an electron discharge tube of the multi-grid type and having a plurality of discharge paths extending from the cathode, each discharge path being at least partially controlled by a common control electrode.

In radio receivers employing the superheterodyne method of reception, the problem is to combine two different oscillations; that is, the oscillations produced by a distant signal received by the antenna and usually amplified in a preceding stage, and the local oscillations produced in the receiver proper for providing the heterodyne action, so that the resulting intermediate frequency oscillations are modulated in the same manner as the distant signal. This action is usually accomplished in a so-called mixer tube used in various well known circuits. In order to simplify the receiver, it has been previously proposed toprovide the function of the local oscillator (heterodyne) and that of the mixer stage within a single tube. This is usually accomplished by using a tube containing several grid electrodes between a cathode and an anode. Upon one of the grids, for example, that next to the cathode, the modulated distant signal may be impressed. By means of two further grids coupled to each other usually by a feed back arrangement, the local heterodyne oscillation is produced, and the latter together with the received signal results in the desired intermediate frequency oscillations which appear in the anode circuit. It is important to generate the local oscillations independently of control by the input or signal voltage. To this end, a screen grid is placed between the control grid and the electrodes serving for the production of the local oscillations. In this .way a tube having six electrodes (hexode) is obtained, which has positioned in the discharge path between the cathode and anode four electrodes thru which current passes. If necessary, still another screen grid (suppressor grid) could be placed in front of the anode, and some other sequence of the electrodes connected tothe input circuit and those serving for the production of local oscillations could be arranged.

The above method of producing oscillations in the current path controlled by the alternating input or signal voltage has a number of practical disadvantages, which become particularly noticeable if the same tube is used for volume control, for example, for the purpose of compensating for fading phenomena due to atmospheric conditions. In this case, the electron current is eventually blocked to such an extent, by the action of the control electrode, that the current density necessary for the production of the local oscillations, is no longer available. V

Similar conditions exist in other circuits. This is true, for example, in a high frequency amplifier stage made regenerative for example by means of feed back, and whose amplification factor is controlled at the same time by varying the grid voltage. Also the so-called homodyne circuit must be mentioned in this connection. As is well known this circuit is characterized by the heterodyning of the received signal on an oscillation produced in the receiver and of a frequency conforming with that of the carrier wave. These last two arrangements differ from the above mentioned mixer circuit in intermediate frequency principally by the value of the frequency with which self excitation or regeneration is produced.

It is an object of my invention to provide an improved tube which will avoid the above disadvantages, particularly if the tube is used for volume control and which has a more favorable electrical separation between the parts of the tube generating the local oscillations and the parts performing the actual mixing operation by constructing a tube having two separate discharge paths from a common cathode and at least one grid electrode common to both discharge paths.

Multi-grid tubes have been provided in which all electrodes are in the same discharge path, or in which the discharge paths are entirely separated except for a common cathode. However, such tubes are not adapted to successfully perform the functions outlined above. It has also been suggested, to place around a single cathode two electrode systems adjacent each other, and to conductingly connect, or to constructively join one of the electrodes or several of the electrodes in the different systems. The present invention differentiates over the arrangement described in that the two discharge paths are not placed side by side, but extend in different directions, preferably displaced to each other. This provides the advantage of a more favorable condition for less coupling of the two systems without the use of special shielding devices, and the further advantage that a short length construction of the tube is obtained, in View of which the electrode system can be easier manufactured and mounted. Furthermore, such an electrode system is practically free from microphonic effects.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims, but the invention itself will best be understood by reference to the'following description taken in connection with the accompanying drawings in which'Figure 1 is a schematic view of an electron discharge device embodying my invention. Figure 2 is a diagrammatic showing of a circuit embodying the tube shown in Figure 1. Figure 3 is a schematic transverse crosssection taken thru a tube made in accordance with my invention and showing the electrode arrangement. Figures 4 and 5 are schematic transverse cross sections of modifications of the tube shown in Figure 3. Figure 6 is a diagrammatic showing of a circuit embodying a still further modification of the tubes shown in the preceding figures.

As shown in Figure l, the tube is provided with a glass bulb or envelope i containing an electron emitting cathode 2, which may be directly or indirectly heated. The cathode is enclosed by. a 7

grid like electrode 3 preferably of cylindrical shape. The other electrodes are positioned in different current paths. The auxiliary anode 4 is placed on one side of the cathode and grid 3 and on the other side is placed the screen grid 5,

' manner.

the control electrode 6, a second screen grid l and the main anode 8. 7

With atube of the type described the circuit shown in Figure 2, as well as others, can beused. The input circuit comprising the inductance L and condenser C fed from the antenna A or from a proceeding stage, is connected between the cathode 2 and the control grid 6, which ishegatively biased by means of the battery Eg. If it is desired to provide automatic volume control, the control grid bias may be made variable and to depend upon the input amplitude in any well known In this case the grid 5 is designed to have a variable mu or amplification factor. The two screen grids 5 and i may be operated at the same positive bias.

, nected to each otherwithin'the envelope or within the base thereby saving one base pin. The auxiliary anode 4 connected to the positive side of the anode battery Ea thru the inductance L,

' is coupled by means of this inductance to the "will be controlled by the grid 3 to vary the frequency of oscillation produced in the auxiliary discharge circuit, and at the same time will be controlled by the signal impressed on the control grid 6. Regarding the operation of the tube, it is pointedout that the voltage of the electrode 6 controls the current distribution between the anode 8 and the first screen grid 5. In other words, the mutual conductance S or steepness of the anodecurrent characteristic will be affected by the'voltage on electrode 6. Since the presence of the second screen grid 1 makes reaction of the alternating anode potential upon the control performance so slight that it can be disregarded, the condition exists that the alternating 7 plate current Ja is equal tothe product of the wave or signal and the heterodyne frequency,

which appears in the anode circuit and is transferred to the subsequent amplifier, which may They are electrically conbe connected across the oscillatory circuit comprising inductor L2 and condenser C2 tuned to the intermediate frequency.

In the oscillatory grid circuit L1, C1 there is connected in series with the coil Li, a resistor R bridged by a condenser C3 for the following reaoscillations are generated, a grid current pro- 7 ducing a voltage drop across resistor R, begins to flow, and consequently the working point or grid bias of. the tube will be shifted into the region ofnegative grid bias thereby stabilizing and limiting the amplitude of the oscillations.

It may furthermore be of advantage to provide the two halves of grid 3 with a difierent mu .or amplification factor. For producing oscillations a high mu is desirable since in this case;

small feed back voltages suflice, and the steady state oscillation amplitude can be adjusted to have small values, especially by means of the action of the resistor R mentioned above. However, for the other discharge path the total usee 1* ful control range is of great importance. This range must be large as compared with the total useful control of the discharge path servingfor the production of local oscillations, in order that the heterodyne oscillations do not cause overload;

and produce distortions, which distortions must be avoided under all conditions because of the upper harmonics thereby developed. For this reason different values of mu (amplification factor) are chosen for the two grid halves.

from 5 to 10 times as large asthe mu at the side of the mixing system. The mu meant is that with referenceto the electrode directly following the respective grid half, thus in the one case, to the mu between .electrodesj3 to 4, and in the other case between electrodes 3 to 5; The requirement of a different mu is especially easy to accomplish if the grid 3 is composed of two halves which are 'conductingly connected to each other, since in this case the current penetration (determined by the width of the mesh or the pitch of the grid) as well as the distance from the cathode can be made of different magnitude.

Figure 3 shows a transverse cross section of the electrode system constructed in accordance with my'invention. In the glass envelope i there is placed the cathode 2, preferably indirectly heated, and enclosed by a concentric cylindrical grid 3. In order to bring the grid surface as close as possible to the cathode surface, it is shaped. as shown and is secured to the supporting rods H by means of two ribs or fins 40. By thisconstruction the production of a homogeneous field is made possible in the proximity of the cathode- At the same time-the ribs or fins i8, which act as shields, improve the decoupling ofthe two discharge paths by their shielding action. The

The mu. at the side of the local oscillation system is made auxiliary anode 4, having the shape of a hater curved plate, is placed at oneside of the control grid. On the other side the electrode 3 is followed by the first screen grid 5, the control grid 6, the second screen grid 1 andthe main anode 8. These electrodes are formed for example, as plane surfaces parallel to each otherr;

' Since, asstated above, the two screen grids 5 and 1 1 can have the same potential applied to them, they can be structurally combined, and may for -example have the shape of a box-formed of a metal mesh, and be mounted on two longitudinaltrode system is shown in Figure 4. The electrode 7 i system mounted within the glass envelope con the supporting wires.

tains a so-called fiat cathode 2| preferably of rectangular cross section. The advantage of the flat cathode isthat a very homogeneous field distribution is formed around it, and that the control electrode can be very closely disposed to the cathode because it can be stretched out between ode insures a favorable decoupling of the two discharge paths. The control grid 22 has the shape of a box of rectangular cross section, formed of two halves having a different width of the mesh. The same box shape is also used for the double screen grid 23 whose surface is twice passed by the discharge current. The second control grid 24, as well as the anode 25, has a U-shaped cross section, which promotes the formation of a homogeneous field and permits the electrodes to be mounted in the center plane of the electrode system. The auxiliary electrode 26 is shaped as a flat plate.

The modification shown in Figure 5 shows the electrode system provided with a. suppressor grid. For the sake of simplicity the same reference characters have been used for the electrodes corresponding with those of Figure 4. The added suppressor grid 21 performs several functions. A negative potential with respect to the anode 25, preferably the cathode potential, is applied to the suppressor grid. Because of this, the suppressor grid prevents secondary electrons from the anode from reaching the preceding screen grid 23. At the same time, the mu of the control grid 22 with respect to the anode 25 is increased and therefore the anode reaction is decreased, i. e. the plate impedance is increased. The suppressor grid furthermore permits the application to the screen grid 23 of the same direct voltage as that applied to the anode 25, while heretofore a lower voltage was usually impressed upon the screen grid, this voltage ordinarily being obtained from a voltage divider. As shown in Figure 5, the suppressor grid is likewise formed into a box shape and surrounds the auxiliary electrode 26, thus including the discharge path between the cathode and the auxiliary anode. Consequently a favorable screening towards the outside is produced, so that the discharge is no longer influenced by disturbing exterior fields.

A further embodiment of a tube coming within the scope of the present invention, is schematically represented in the circuit diagram of Figure 6. For the sake of simplicity, identical reference characters have been used here for the elements conforming with those in Figure 2. The novel feature in the tube is in that the two halves 3', 3" of the innermost grid 3 are not conductingly connected to each other, but capacitively by means of a condenser K. The condenser is suitably mounted in the interior of the tube or in the socket, and each grid half is provided with an insulated lead. This measure appears to be expedi- In addition the flat cathent, where the two halves 3', 3" altho having the same alternating voltage applied to the two halves, have different direct voltages applied to them. This case occurs when'the innermost grid 3* is intended to be used for volume control. The

high frequency voltage supplied by the input'circuit LC is impresse upon the control grid 6 only, while the variable control voltage source designated by Er is applied to the grid half 3' as well as to the second control grid 6, or the control voltage may beapplied only to the grid 3. In the first case, the controlling action will be more efiective. In the lead to the grid half 3', a resistance W is inserted, in which the sameradio frequency voltage'wil be developed as that in the tuned circuit L1 C1.

While I have indicated the preferred embodiment of my invention of which I am now aware and have also indicated only one specific application for which my invention may be employed, it is apparent that my invention is by no means limited to the exact forms illustrated or the use indicated, but that many variations may be made in the particular structure used and the purpose for which it is employed without departing from the scope of my invention as set forth in the appended claims.

What I claim as new is,

1. An electron discharge tube having a thermionic cathode, a grid electrode surrounding said cathode and provided with oppositely extending longitudinal fins, a plurality of grids and an anode positioned on one side of said cathode for providing a main discharge path between said cathode and said anode, an auxiliary anode placed on the opposite side of said cathode from the main anode to provide a second discharge path between said cathode and said auxiliary anode, the fins on said grid shielding the two discharge paths from each other.

2. An electron discharge tube having a thermionic cathode, a grid electrode surrounding said cathode, a main anode positioned on one side of said cathode, a control electrode between said main anode and said cathode, and a box-shaped electrode surrounding only said control electrode and permitting the passage of current between said cathode and said main anode, an auxiliary anode placed on the opposite side of said cathode from said main anode to provide a discharge path between said cathode and said auxiliary anode.

3. An electron discharge tube having a thermionic cathode, a grid electrode surrounding said cathode, a main anode positioned on one side of said cathode, a control electrode between said main anode and said cathode, and a box-shaped electrode surrounding said control electrode, and an auxiliary anode placed on the opposite side of said cathode from said main anode, and a suppressor grid placed between said main anode and the other electrodes in said discharge tube and surrounding all of the other electrodes in said tube.

4. An electron discharge tube having a thermionic cathode, a grid electrode surrounding said cathode, a main anode positioned on one side of said cathode, a control grid electrode between said main anode and. said cathode, and a box-shaped grid electrode surrounding said control electrode, and permitting the passage of electrons from said cathode to the main;-anode, an auxiliary anode: .-:-placed on the opposite side of said cathode from said main; anode, and a suppressor grid placed between :saidprincipalanode and the iother-e1ec- -trodes in said discharge tube and surroundingall of the other electrodes in: said tube,- one of the :w.

.; between said main anode and the 'Iotherelectrodes igrid electrodes between saidmainanode and said --cathode having a variable mu characteristic.

f 5. An electron discharge "tube havinga thermionic cathode, a grid'electrode surrounding-said thermionic cathode, a main anode positioned' on one ,side of said thermionic cathode, a-contro1 electrodepositioned between said= cathode and. saidsmain anode and a screen electrode surroundr :S aid cathodeand-lithe anodes;

:1 6;, Anelectron discharge tube having a-thermionic cathode, a grid electrode surrounding said i thermionic cathode, a main anode positioned on one side of-rsaidthermionic cathode, a control electrode positioned between said cathode and said main anode, :a screen-electrodesurrounding said control electrode; an auxiliary electrodeiposl- 'tioned on the other side ofqsaid ica-thodei'romisaid main electrode whereby oppositely. extending dis- 'charge paths-"are provided between-.fsaid cathode and-the anodes, and a. suppressor :grid: positioned inthe tubeand surrounding all of :the otherselectrodes within said tube. V

7.4m electron discharge:tubeahavingaazthermi-f onic cathode, a grid electrode surrounding: said electron discharge paths -are ,Iprovided:-.- between said cathode andsaid: anodes; ,andzoppositely'disposed longitudinal fins 1 extendingznoutwardly 'from said grid electrode, said fins being positionedperpendicularly to-the electrondischarge paths between, said cathodeand saidanodes' to" shield the two electron discharge paths from each other.

' KARLLSTEIMEL.

-. cathode, y a main anodes-positioned"onionezside of V said, cathode, a control :electrodei"betweencsaid main anode and said cathode; anaauxiliary-anode placed on the oppositerside' oflsaidscathoderfromi said main anode wherebytworoppositely:disposed 

